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//! Flexible and lazy layouting of boxes.
use crate::size::{Size, Size2D};
use super::{BoxLayout, ActionList, LayoutSpace, Alignment, LayoutResult, LayoutError};
/// A flex layout consists of a yet unarranged list of boxes.
#[derive(Debug, Clone)]
pub struct FlexLayout {
/// The sublayouts composing this layout.
pub units: Vec<FlexUnit>,
}
/// A unit in a flex layout.
#[derive(Debug, Clone)]
pub enum FlexUnit {
/// A content unit to be arranged flexibly.
Boxed(BoxLayout),
/// A unit which acts as glue between two [`FlexUnit::Boxed`] units and
/// is only present if there was no flow break in between the two surrounding boxes.
Glue(BoxLayout),
}
impl FlexLayout {
/// Create a new flex layout.
pub fn new() -> FlexLayout {
FlexLayout {
units: vec![],
}
}
/// Create a new flex layout containing just one box.
pub fn from_box(boxed: BoxLayout) -> FlexLayout {
FlexLayout {
units: vec![FlexUnit::Boxed(boxed)],
}
}
/// Add a sublayout.
pub fn add_box(&mut self, layout: BoxLayout) {
self.units.push(FlexUnit::Boxed(layout));
}
/// Add a glue layout which can be replaced by a line break.
pub fn add_glue(&mut self, glue: BoxLayout) {
self.units.push(FlexUnit::Glue(glue));
}
/// Add all sublayouts of another flex layout.
pub fn add_flexible(&mut self, layout: FlexLayout) {
self.units.extend(layout.units);
}
/// Whether this layouter contains any items.
pub fn is_empty(&self) -> bool {
self.units.is_empty()
}
/// Compute the justified layout.
pub fn finish(self, ctx: FlexContext) -> LayoutResult<BoxLayout> {
FlexFinisher::new(self, ctx).finish()
}
}
/// The context for flex layouting.
#[derive(Debug, Copy, Clone)]
pub struct FlexContext {
/// The space to layout the boxes in.
pub space: LayoutSpace,
/// The flex spacing between two lines of boxes.
pub flex_spacing: Size,
}
/// Finishes a flex layout by justifying the positions of the individual boxes.
#[derive(Debug)]
struct FlexFinisher {
units: Vec<FlexUnit>,
ctx: FlexContext,
actions: ActionList,
dimensions: Size2D,
usable: Size2D,
cursor: Size2D,
line_metrics: Size2D,
line_content: Vec<(Size2D, BoxLayout)>,
glue: Option<BoxLayout>,
}
impl FlexFinisher {
/// Create the finisher from the layout.
fn new(layout: FlexLayout, ctx: FlexContext) -> FlexFinisher {
let space = ctx.space;
FlexFinisher {
units: layout.units,
ctx,
actions: ActionList::new(),
dimensions: match ctx.space.alignment {
Alignment::Left => Size2D::zero(),
Alignment::Right => Size2D::with_x(space.usable().x),
},
usable: space.usable(),
cursor: Size2D::new(space.padding.left, space.padding.top),
line_metrics: Size2D::zero(),
line_content: vec![],
glue: None,
}
}
/// Finish the flex layout into the justified box layout.
fn finish(mut self) -> LayoutResult<BoxLayout> {
// Move the units out of the layout.
let units = self.units;
self.units = vec![];
// Arrange the units.
for unit in units {
match unit {
FlexUnit::Boxed(boxed) => self.boxed(boxed)?,
FlexUnit::Glue(glue) => self.glue(glue),
}
}
// Flush everything to get the correct dimensions.
self.newline();
Ok(BoxLayout {
dimensions: if self.ctx.space.shrink_to_fit {
self.dimensions.padded(self.ctx.space.padding)
} else {
self.ctx.space.dimensions
},
actions: self.actions.into_vec(),
})
}
/// Layout the box.
fn boxed(&mut self, boxed: BoxLayout) -> LayoutResult<()> {
let last_glue_x = self.glue.as_ref()
.map(|g| g.dimensions.x)
.unwrap_or(Size::zero());
// Move to the next line if necessary.
if self.line_metrics.x + boxed.dimensions.x + last_glue_x > self.usable.x {
// If it still does not fit, we stand no chance.
if boxed.dimensions.x > self.usable.x {
return Err(LayoutError::NotEnoughSpace);
}
self.newline();
} else if let Some(glue) = self.glue.take() {
self.append(glue);
}
self.append(boxed);
Ok(())
}
/// Layout the glue.
fn glue(&mut self, glue: BoxLayout) {
if let Some(glue) = self.glue.take() {
self.append(glue);
}
self.glue = Some(glue);
}
/// Append a box to the layout without checking anything.
fn append(&mut self, layout: BoxLayout) {
let dim = layout.dimensions;
self.line_content.push((self.cursor, layout));
self.line_metrics.x += dim.x;
self.line_metrics.y = crate::size::max(self.line_metrics.y, dim.y);
self.cursor.x += dim.x;
}
/// Move to the next line.
fn newline(&mut self) {
// Move all actions into this layout and translate absolute positions.
let remaining_space = Size2D::with_x(self.ctx.space.usable().x - self.line_metrics.x);
for (cursor, layout) in self.line_content.drain(..) {
let position = match self.ctx.space.alignment {
Alignment::Left => cursor,
Alignment::Right => {
// Right align everything by shifting it right by the
// amount of space left to the right of the line.
cursor + remaining_space
},
};
self.actions.add_box_absolute(position, layout);
}
// Stretch the dimensions to at least the line width.
self.dimensions.x = crate::size::max(self.dimensions.x, self.line_metrics.x);
// If we wrote a line previously add the inter-line spacing.
if self.dimensions.y > Size::zero() {
self.dimensions.y += self.ctx.flex_spacing;
}
self.dimensions.y += self.line_metrics.y;
// Reset the cursor the left and move down by the line and the inter-line spacing.
self.cursor.x = self.ctx.space.padding.left;
self.cursor.y += self.line_metrics.y + self.ctx.flex_spacing;
// Reset the current line metrics.
self.line_metrics = Size2D::zero();
}
}
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